Fishermen in Hawaiʻi and other parts of the world have long known that tunas and other pelagic fishes are attracted to floating objects. Fishermen have benefited from this behavior by fishing around floating logs, nets, debris and other flotsam. Hawaiʻi has capitalized on this phenomena by placing Fish Aggregation Devices (FADs) in the waters surrounding the Hawaiian Islands. In these waters, schools of tunas and other important pelagic fishes such as dolphin-fish (mahi-mahi), wahoo (ono), and billfishes can be induced to congregate and remain for periods of time in an area so that fishers can easily locate them. Thus, the FADs are used to "attract" and "hold" pelagic fishes in areas to enhance fishing.
These particular FADs are equipped with acoustic receivers for monitoring the presence of fish tagged with acoustic transmitters.
note: Please do not rely on these buoys to check your position. Most buoys have only been located to the nearest 0.1 minute (6 seconds). In addition, each buoy has a watch circle that can be as much as 1 mile in diameter.
info:
http://www.hawaii.edu/HIMB/FADS/
http://www.hawaii.edu/HIMB/sharklab/